Prior Art
Many types of toroidal coil winding machines are available on the market, and one typical coil winding device is disclosed in U.S. Pat. No. 3,400,894 where a split-ring, breakaway wire-carrying shuttle 22 interlinked with a toroidal core 20, is provided with an outwardly facing peripheral groove within which wire is wrapped during a loading operation. The shuttle is supported on a plurality of support sheaves 49, 51, 52 and 53, all rotatably mounted on an adjacent head assembly 21. At least one of these sheaves if rotatably driven to supply traction drive for high speed rotation of the shuttle 22. The interlinked core 20 is likewise supported and rotatably driven at a slower speed on a core holdler assembly 19. These various parts are illustrated in the figures of U.S. Pat. No. 3,400,894, and are indicated by the same reference numerals in the figures hereof.
U.S. Pat. No. 3,601,325 describes the disadvantages of conventional shuttles 16 carrying sliders 17 for sliding movement about their peripheries. These sliders have traditionally been employed to control the delivery of wire wound in the outwardly facing peripheral groove of the shuttle itself, by retarding its release and thereby maintaining its tension during the winding operation. The slider progresses slowly backward around the periphery of the shuttle during the winding operation, impelled by the unwrapped segment of wire being drawn from the shuttle and wound around the toroidal core during the winding of each turn of wire thereon.
While these conventional sliders successfully maintain tension on the stored wire, they require precision machining of the shuttles to accommodate them and they increase the overall cross-sectional area of the shuttle, thereby limiting the minimum internal diameter of toroidal cores which can be wound through the use of such slider-carrying shuttles. For this reason, U.S. Pat. No. 3,601,325 discloses a proposed "sliderless shuttle " carrying an elastic belt 18 encircling a major portion of the shuttle's periphery and diverging from the shuttle at a point 20A just before it reaches the toroidal core, passing around an idler roller and returning to the shuttle just beyond the core, at a point 20B.
While this elastic-belt wire-retainer serves to reduce the overall cross-section of the shuttle assembly passing through the toroidal core, it exhibits several disadvantages. For example, the belt tension varies with rotational velocity of the shuttle, since the belt's forward velocity is essentially matched to the shuttle's angular velocity. At higher speeds, centrifugal force urges the belt away from the stored wire carried in the outwardly facing peripheral groove of the shuttle, precisely when greater retaining force is desired to avoid centrifugal release of the stored turns of wire. At the same time, this radial expansion tendency of the belt at higher speeds reduces the frictional force exerted by the belt on the turn of wire being drawn from the shuttle. Again, the forces exerted by the stretched elastic belt on the rearward sector of the shuttle tend to deform the shuttle and may cause it to jump from its supporting sheaves and fly off, spinning in its plane of rotation, endangering nearby personnel as the last stored turns of wire are drawn from the shuttle. If outward radial acceleration forces on the retaining belt sufficiently reduce the elastic forces tending to retain the belt on the shuttle, the belt itself may be released and may fly off, removing the wire retaining structure entirely and allowing loose coils of wire to spill before the machine can be shut down. Finally, the elastic belt of U.S. Pat. No. 3,601,325 passes directly around the core on the core holder, obscuring the operator's view. In many situations these various disadvantages are not encountered, but their likelihood in certain situations makes a more reliable sliderless shuttle and protective wire guide mechanism highly desirable in the toroidal coil winding field.